This invention relates generally to an initiator charge for use in an igniter assembly of an inflator device for an inflatable restraint system. More particularly, the invention relates to a single increment initiator charge effective to ignite an associated pyrotechnic composition.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion” that is inflated or expanded with a gas when a vehicle experiences a sudden deceleration, such as in the event of a collision. Such airbag restraint systems normally include: one or more airbag cushions, housed in an uninflated and folded condition to minimize space requirements; one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden deceleration of the vehicle; an activation system electronically triggered by the crash sensors; and an inflator device that produced or supplies a gas to inflate the airbag cushion. In the event of a sudden deceleration of the vehicle, the crash sensors trigger the activation system which in turn triggers the inflator device which begins to inflate the airbag cushion in a matter of milliseconds.
Many types of inflator devices have been disclosed in the art for inflating one or more inflatable restraint system airbag cushions. Such inflator devices typically include: an igniter assembly; multiple combustible pyrotechnic compositions; and a housing for containing the igniter assembly and the one or more pyrotechnic compositions. The igniter assembly generally includes an eyelet having one or more electrically conductive pins connected to a bridgewire to form a closed electrical circuit. The bridgewire is maintained in intimate contact with an electrically ignitable initiator charge that is held or contained within a charge holder or cup. In the event of a collision, the activation system directs an electrical current through the conductive pins of the igniter assembly to the bridgewire. The bridgewire ignites the initiator charge which in turn ignites an associated pyrotechnic composition such as an igniter composition or a gas generant composition to begin production of inflation gas and, thereby, inflation of an associated or corresponding airbag cushion.
Various initiator charges have been disclosed in the art for igniting an associated pyrotechnic composition. Typically, in order to meet industry and federal safety standards, such initiator charges include two separate compositions or increments: an igniter composition or increment that is generally electrothermally conductive and ignitable; and an enhancer or booster composition or increment that increases the temperature of combustion and pressure output of the igniter assembly. Generally, such compositions are loaded sequentially into the charge holder with the igniter composition or increment placed in intimate contact with the bridgewire to facilitate firing of the inflator device.
A number of igniter compositions or increments have been disclosed in the art for use in inflator devices such as are used in inflatable restraint systems. One such igniter composition or increment includes a metal or metal fuel such as zirconium or titanium and an oxidizer such as potassium perchlorate. Such igniter compositions are particularly desired because they generally readily ignite upon the application of an electrical current. However, for automotive applications, such as in an inflatable restraint system, such igniter compositions or increments typically do not generate sufficient heat and/or pressure to ignite an associated pyrotechnic composition. Thus, such igniter compositions or increments are generally used in combination with a separately compounded enhancer or booster composition or increment.
The enhancer or booster composition or increment generally serves to increase the temperature of combustion and/or to increase the pressure generated during the combustion of the initiator charge. Suitable enhancer or booster compositions or increments may typically include metal hydrides such as titanium hydride or zirconium hydride in combination with an oxidizer compound such as potassium perchlorate. Generally, such enhancer or booster compositions or increments do not possess sufficient electrothermoconductive properties to adequately ignite when exposed to an electrical current passed through an associated bridgewire. Thus, such enhancer or booster compositions or increments are typically used to supplement the igniter composition or increment.
The sequential loading of two separate compositions or increments requires additional process steps such as separate compounding, loading and compression steps to form an initiator charge effective to ignite an associated pyrotechnic composition. Such additional steps generate increased manufacturing expenses such as in the form of added equipment, labor, quality assurance analysis and process time. Moreover, the materials typically employed in both the igniter composition or increment and the enhancer or booster composition or increment can be difficult or dangerous to load and can pose significant safety concerns for those handling such materials. Thus, compounding and loading two separate compositions or increments increases the level of risk to which workers are exposed.
In view of the above, there is a need and a demand for a single increment initiator charge that meets the requirements for a multiple increment initiator charge. In particular, there is a need and a demand for a single increment initiator charge that is effective to reproducibly and reliably ignite an associated pyrotechnic composition. There is a further need and a demand for a single increment initiator charge that is more cost-effective and safer to manufacture than commercially available initiator charges including multiple, sequentially loaded compositions or increments.